Multiple heating element



March 24, 1953 A. J. HucK E1- AL MULTIPLE HEATING ELEMENT Filed June 17, 1950 i. al

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Patented Mar. 24, 1953 MULTIPLE HEATING ELEMENT Alfred J. Huck and John J. Kueser, St. Louis, Mo., assignors to Knapp-Monarch Company, St. Louis, Mo., a corporation of Delaware Application June 17, 1950, Serial No. 168,744

l. Claim.

This invention relates to a heating element comprising two or more resistance type heating wires so that any one or a combination of the wires can be energized for securing different degrees of heat from the heating element.

One object of the invention is to provide a multiple heating element in which all the resistance wires are contained in a single sheath so that when any one or any combination of the resistance wires is energized, the heating area remains the same. This is particularly desirable in connection with an electric hotplate or range wherein the heating element is usually wound in spiral formation to substantially cover the bottom of a cooking utensil. Heretofore, it has been the general practice to provide the resistance elements in separate sheaths and spirally Wind the sheaths, one of small diameter and the other of large diameter so that one may be located in the central opening of the other one. This is objectionable, however, as a given cooking utensil placed on such a heating element will have a different area thereof heated by one heating element as compared with the same utensil being heated by the other heating element, and usually the overall size or diameter of the entire heating element assembly must be so large that small pans do not cover the entire area.

Accordingly, another object of our invention is to provide a heating element which can have all the resistance wires in a single sheath and the sheath can be held down to a minimum size, with substantially even heating over the entire area regardless of what heating resistance wire or combination of wires is energized.

Still another object is to provide the resistance wires in the form of coils which are concentric as distinguished from side-by-side relationship as shown, for instance, in the Tuttle Patent No. 2,456,343 issued December 14, 1948.

A further object is to provide a concentric resistance coil arrangement so as to simplify the formation of the heating element.

Still a further object is to provide a heating element that has concentric elements Within the sheath thereof and the top of the sheath flattened for greater area contact with the cooking utensil.

With these and other objects in view, our invention consists in the construction, arrangement and combination of the various parts of our multiple heating element whereby the objects contemplated are attained, as hereinafter more fully set forth, pointed out in our claim and illustrated in the accompanying drawings, wherein:

Figure 1 is a sectional view through part of a machine of the kind shown in the Smith Patents No. 1,951,176 of March '13, 1934, and No. 1,987,915 of January 15, 1935, for forming heating elements of the type having a coil of resistance wire-lled with and embedded in a solid cylinder of argillous material. This figure illustrates a first step in the process of forming our improved heating element comprising the extrusion of a first resistance coil and a cylinder of argillous material in which it is imbedded.

Figure 2 illustrates the second step in the forming thereof wherein a second coil of resistance Wire is extruded with a layer of argillous material around the first cylinder of argillous material and its resistance coil.

Figure 3 is a similar sectional view showing a modification in which both resistance coils are embedded in an argillous core at the same time.

Figure 4 is a part elevation and part sectional view of the pair of resistance coils and their core of argillous material being inserted into a metallic sheath.

Figure 5 is a plan View of the sheath after it is formed in spiral shape and its top surface Iiattened so as to make it adaptable for heating a cooking vessel, an electric wiring diagram being also illustrated in this gure.

Figure 6 is an enlarged sectional view on the line 6--6 of Figure 5, and

Figure '7 is a similar sectional view showing the shape of the parts before the sheath has been flattened for better contact with the cooking vessel.

On the accompanying drawing we have used the reference numeral I0 to indicate a hopper for argillous material I2, which hopper has a discharge nozzle I4. As disclosed in the abovementioned Smith patents, the argillous material I-2 is under pressure so that it is extruded from the nozzle I4.

Depending within the hopper I0 is a guide tube I6 for acoil of resistance wire I8, the lower end of which is lled with and embedded in a core I2a of the argillous material I2 as it is extruded from the nozzle I4, the extrusion movement also serving to draw the resistance coil IB downwardly through the tube I6.

The resistance coil I8, as shown in Figure 2, and the core I2a are then placed in a guide tube 20 in a hopper I 0a having a discharge nozzle I4a of somewhat larger diameter. A guide tube 22 is provided for a second resistance coil 24 and the argillous material l2 in the hopper Illa, is extruded to form a tubular core as indicated at 12b. This core embeds the resistance coil 24, propels it downwardly in the guide tube 22 and encloses it, the core 52h completely surrounding the core [2a. The final result is a solid argillous cylinder having the outer diameter of the coil |21) and having the pair of concentric resistance coils I8 and 24 completely embedded therein.

An alternative method of forming the resulting product is shown in Figure 3 wherein the hopper ma and its nozzle Ella have the guide tubes I6 and 22 both depending therein, and the resistance coils I8 and 24 are fed downwardly into the argillous material l2 to form a single core I2C with the two resistance coils embedded therein and concentrically related to each other.

After the cores ma and l2b or E20 are formed, they are permitted to dry slightly, the argillous material I2 being moist and in plastic condition as disclosed in the Smith patents. Drying is permitted just long enough to permit handling and subsequent insertion into a metallic sheath 26 as shown in Figure ll, the sheath being straight and thus permitting free entry of the core and resistance coils, and the inside diameter of the sheath being slightly greater than the outer diameter of the core or cores to permit ready assembly.

The heating element is then fired to produce a ceramic of the argillous material after which it is formed to any .desirable pattern such as a spiral as shown in Figure 5. iThe resulting crosssection is shown in Figure '7. rlThe top surface of the sheath may then be iiattened as indicated at 28 in Figure 6 by a die hitting operation which will deform the sheath and the cores and resistance coils to some extent. This also compacts the argillous material within the sheath which has the effect of increasing its dielectric strength. The iiring, forming and flattening process is more fully disclosed and claimed in our copending application, Serial No. 165,892 led June 3, 1950.

While we have shown only two concentric resistance coils, it is obvious that three or more may be provided by extending the steps beyond Figures 2 and 3 with the addition of more guide tubes and more resistance coils of greater diameter. The completed heating elements may be mounted after forming and connected with the electric currenty such as in the manner disclosed in Figure 5. The wires i8 and 24 are connected together at 39 and connect with one line wire 32. The other ends of the wires I8 and 24 are connected with the usual type of control switch 34 and another line wire 36 connects with this switch. The switch is then designed to energize, for instance, the wire i8 for low heat, the wire 24 for medium heat and both wires for high heat. This arrangement necessitates only three connections as distinguished from two connections to each resistance coil in the former types of heating elements referred to.

We are aware of prior constructions wherein a sheathed heating element has resistance Wires arranged side-by-side. Some warpage of the sheath occurs in this type of element if one coil such as the medium heat coil carries a considerably higher wattage than the other coil (low heat coil). In our concentric design with one coil inside the other, no twisting or warping of the tube results if the outer coil carries a higher wattage than the inner coil. Twisting or warping of the sheath represents a serious disadvantage on a stove surface unit because when the top surface of the sheath twists or warps, it does not remain in the same plane and the heating unit does not transfer its heat efliciently to the bottom of the vessel which in that case would not contact the entire upper surface of the heating element. It is thus obvious that the provision of a sheathed heating element that does not warp is important and when the coils are concentric as in our design, there is no tendency for the sheath to Warp.

When our heating element is used in a stove burner for example, the continuous length of the sheath is eiiiective for heat transference to the cooking vessel regardless of whether the wire I8, the wire 9&3 or both wires are energized. The arrangement also simplies manufacture in that only a single sheath has to be handled and formed.

Some changes may be made in the construction and arrangement of the parts of our device without departing from `the real spirit and purpose of our invention, and it is our intention to cover by our claim any modified forms of structure or use of mechanical equivalents which may be reasonably included within its scope.

We claim:

In a heating element construction, a tubular metallic sheath, a plurality of concentrically arranged resistance coils therein, and fired ceramic insulating material filling said coils and sheath, spanning the distance between the coils and spanning the distance between the outer coil and said sheath, one surface of said sheath being fiattened for increasing the contact area with a cooking vessel, the portions of said coils adjacent said one surface being proportionally iiattened one within the other thereby and the red ceramic being reshaped and compacted thereby between said coils, said return lead and said sheath, said material holding said coils spaced from each other and the outer coil spaced from said sheath.

ALFRED J. HUCK. JOHN J. KUESER.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,469,588 Onwiler Oct. 2, 1923 1,997,844 Wiegand Apr. 16, 1939 2,455,186 McCormick Nov. 30, 1948 2,456,343 Tuttle Dec. 14, 1948 2,494,333 Daly Jan. 10, 1950 

